Image display systems based on spatial light modulators (SLMs) are increasingly being used as an alternative to image display systems based on cathode ray tubes. As used for image display applications, SLMs are arrays of pixel-generating elements that emit or reflect light to an image plane. The pixel-generating elements of the SLM are often themselves referred to as "pixels", as distinguished from pixels of the image. This terminology is clear from context, so long as it is understood that more than one pixel of the SLM can be used to generate a pixel of the image.
The pixels of the SLM are individually addressable, such that the image is defined by which pixels are on or off at a given time. The addressing of each pixel is in response to pixel data representing the on or off state of each pixel. Moving images can be generated by readdressing the SLM with data for successive frames. Greyscale images can be created with various modulation schemes, and color images can be created by filtering the emitted or reflected light.
Pixel data to be displayed by an SLM-based display system may be obtained by digitizing an analog input signal or may be delivered to the display system already in digital form. In either case, various pixel data processing tasks may be performed to improve the quality of the image. One such task is progressive scan conversion, where data from interlaced fields is used to generate data for non-interlaced frames. Another such task is vertical scaling, where data having one vertical resolution is used to generate data for a different vertical resolution.
The SLM may have its pixels arranged in either of two basic patterns. One pattern is referred to as the "Manhattan" or "square grid" pattern, in which the pixels are both vertically and horizontally aligned. A second pattern is the "staggered" pattern, in which the pixels of adjacent rows are offset like bricks of a wall.
For SLMs having pixel arrays with the staggered pattern, the perceived horizontal resolution is better than with the square grid pattern. However, the pixel processing tasks for SLMs with staggered pixels present problems not encountered with SLMs with square grid pixels. In general, for tasks involving generation of new lines of pixels, such as progressive scan conversion or scaling, pixel values for each new line are calculated from pixel values on lines above or below the new line. For square grid pixels, pixel values directly above or below the new pixel values are used for the calculations. However, for staggered pixels, the pixel values on the lines above or below the new pixel values are offset and the calculations must be different.